The human skin is covered with two to three million sweat glands. These are used day and night to convey moisture to the surface of the skin and thus to prevent the organism from overheating. The sweat which emerges ensures the necessary cooling as it evaporates.
In the normal case, 0.5 to 1 liter of sweat are produced daily. In cases of strain on the body and increased metabolism, it may be many times the amount of produced sweat. The course of the development of a human involves the formation of two types of sweat glands. From birth onwards, a person has only ecrine sweat glands (small sweat glands) but the onset of puberty sees the formation of the apocrine sweat glands (large sweat glands), primarily in the area of the armpits and in the anal and genital regions. Only the latter lead, in connection with skin bacteria which decompose the odorless sweat, to the known unpleasant odors. The odor of sweat is person-specific and is pronounced to different degrees for each person. For most people, simple washing can only achieve a short-term improvement, meaning that often enough it is not possible without the use of deodorant active ingredients.
In order to achieve a deodorant effect, there are various ways which, in the normal case, are used in combination.
The use of antiperspirants which prevent the production of sweat by blocking the openings of sweat glands has been known for a long time. Use is usually made here of aluminum and aluminum/zirconium salts. According to the latest findings, the reduced sweat production has no effect on the organism since the “cooling effect” largely takes place via the “sweating” of the other areas of the skin (ecrine glands). The inhibition of bacterial growth as a result of bacteriostats in the area of the skin zones covered with apocrine sweat glands is not acceptable and sometimes leads to severe irritations and allergic reactions.
The alcohol (ethanol) which is present in many of the conventional deodorant products also acts as bacteriocide. Here too, side-effects are often common.
To mask the odor of sweat, fragrances or perfume substances are usually present in the deodorant preparations. Some of these also have a bacteriostatic effect, but with many of them users have similar side-effects as the bacteriostats.
Due to the mode of action described above and the side-effects associated therewith, the attempts to develop deodorant products which do not have side-effects are great. The trend is thus clearly in the direction of a combination product in which a deodorizing and antiperspirant effect accompanies a skincare effect.
Such care deodorants based on O/W (oil-in-water) emulsions have already entered the market, but handling, that is to say application to the skin, still leaves a lot to be desired.
For the application of antiperspirants, many consumers favor the so-called pump atomizer product form since the contents can be applied from this in finely dispersed form to the armpit region without the fingers having to come into contact with them. Compared with aerosols, there is also the ecological advantage that pump atomizers function without the use of propellants (liquefied gases). Transparent and translucent products are preferred by many consumers primarily for aesthetic reasons. The combination of this feature with the wish for highly effective antiperspirant products has hitherto only been realized with aqueous alcohol formulations. These formulations consist virtually only of water and alcohol as medium, deodorant and antiperspirant agents as active ingredients, and perfume, solubility promoters and thickeners (in most cases based on carbohydrate) as additional agents. They are perceived by the consumer as being fresh and cooling, but are at the same time burdened with a whole series of shortcomings. For example, the application primarily to freshly shaved skin is associated with incompatibilities as a result of the alcohol content. A further significant disadvantage is the fact that relatively large amounts of oil cannot be incorporated into such systems. As a result of the high content of antiperspirant salt required for a highly effective performance, a white residue remains on the skin following application, which is perceived as highly undesirable by the consumer. As a result of the absence, brought about technologically, of a sufficiently large oil phase however, this cannot be concealed. Moreover, the use of carbohydrate thickeners leads to a certain stickiness of the product after the alcohol has evaporated. In summary, it may be said that aqueous alcohol formulations are not suitable as a base for the incorporation of high contents of antiperspirant agents (aluminum or aluminum/zirconium complexes).
The solution to all of these disadvantages has been a long time coming. Only recently have also cosmetically pleasing alcohol-free-transparent products been possible which are based on so-called microemulsions. These have the great advantage that even relatively large amounts of various oils—with all of the above-described positive effects for the consumer—can be stably incorporated. Formulations of this type are in principle obtainable by means of phase-inversion temperature technology (PIT) or high-pressure homogenization. The necessary stability of the emulsifier system to high concentrations of antiperspirant salts, however, places high requirements on the formulating skill of the product developer. The use of microemulsions in the cosmetic sector is described in detail in EP 0814752.
For the application of antiperspirants, many consumers favor the product form of the so-called pump atomizer which allows the contents to be applied from it to the armpit region in finely distributed form without the fingers having to be brought into contact with it. Compared with aerosols, there is also the ecological advantage that pump atomizers do not use propellants (liquefied gases). However, a uniform drop size and even spray image cannot be achieved using conventional atomizer pumps since many formulations with a high content of antiperspirant agents, especially ones based on an aqueous alcohol base, have a tendency to form crystals when the atomizer is not often used and represent a high risk of blockage for the nozzle. This hinders or prevents the product from coming out. On the other hand, the consequence of excessively large drops is the running down of the formulation (dripping effect), as a result of which the application is perceived as unpleasantly wet and troublesome.